Ten years of research on tail biting - tail lesions in the slaughter-house
Laura Boyle, Roberta D’Alessio & Keelin O’Driscoll tell us about their research on tail biting over the past decade, focusing specifically on tail lesions in the slaughter-house.
The biggest risk factor for tail biting in pigs is the presence of an undocked tail. This quickly becomes obvious when producers try to transition from rearing docked, to undocked pigs. If no adjustments to management or housing are made there are often many more tail-biting outbreaks than are manageable with many pigs suffering shortening of their tail length. As over 99% of Irish pigs have their tails docked soon after birth, we remove the single biggest risk factor for tail biting from our farms. The proportion of docked pigs in Ireland has not changed meaningfully since we carried out our first research in 2010. This is in spite of significant research, advisory and regulatory focus on tail docking and tail biting in the intervening years.
In the past 13 years we’ve conducted numerous experimental trials with docked and undocked pigs in the Teagasc Pig Research Facility as well as a range of factory based studies looking at tail lesions. This allows us to track changes in tail lesion score prevalence and severity over time. In this article we will compare our most recent factory survey of tail lesions with prevalence and severity data from 2010 (the first Irish factory survey of tail lesion prevalence), 2012, 2014, and 2015. In all these studies we categorised tail lesions from mild to severe, i.e. those which are caused undisputedly by tail biting. We refined the scoring system over the years to improve the accuracy of our measurements, by increasing the amount of detail in our definitions for each level of damage on the system, and separating out bruising from teeth marks. However all the data from our previous studies can be condensed in the following way:
- No visible damage
- Mild lesions: minor skin damage, including bruises, up to evidence of teeth marks with breakage to the skin; however no swelling or inflammation present
- Severe lesions: Breakage to the skin with swelling and signs of infection, fresh partial or complete tail loss accompanied with pus or necrotic tissue. We also included severe tail loss with evidence of scar tissue where the tail would have been (as this is indicative of extreme biting when the pig was younger)
Details of the surveys
The study in 2010 was carried out by Dr. Dayane Teixeira and is our largest and most comprehensive to date, involving scoring of 21,272 carcases from three Irish slaughterhouses. It provided the first detailed snapshot of tail condition in Ireland, and serves as a baseline against which we can evaluate progress over the years. This is because it was carried out prior to the emphasis that the EU started placing on funding research into tail biting and compliance with legislation, about 10 years ago. The next survey was carried out in 2012, in a single slaughterhouse over 1 week, yielding 3,422 tail scores. Following this, former Walsh Scholar Dr. Nienke van Staaveren carried out a series of slaughterhouse studies. In 2014 she collected data from two abattoirs, and gathered data from 61 farms, yielding 13,133 tail records. In 2015 she visited 31 Irish pig farms to assess tail lesions and damaging behaviours for the DAFM funded PigWelFind project, and followed up each farm visit with assessments of carcass tail lesions in the factory. This involved travelling to four Irish slaughterhouses where she obtained data from 6,327 carcases. Finally, between 2020 and 2022 current Walsh Scholar, Roberta D’Alessio conducted a similar exercise with batches of slaughter pigs from 22 farms as part of the PigNoDock project, yielding data from 5,499 carcases, and 3 slaughterhouses.
Results
The pattern of tail lesion prevalence and severity recorded during each of the five experiments is in Figure 1. The pattern of lesion prevalence over time can be understood by observing the green columns, which represent the proportion of tails with no visible evidence of biting. This was approximately 40% of carcases in 2010, it reduced below 30% between 2012 and 2015, but rose again to just over 40% in 2020-2022.
Figure 1. Prevalence of lesion severity on carcase tails observed during slaughterhouse inspections between 2010 and 2022
However, when it comes lesion severity, the story is not as positive. Although the proportion of undamaged tails was similar in 2010 and 2020- 2022, the proportion of tails that had severe damage was much higher – 6.9% in the recent survey, compared with only 1.3% in 2010. Indeed the proportion of tails with severe lesions was significantly lower in all other surveys, with the next highest proportion being 3.1% in 2015.
The pattern of lesion prevalence in our most recent survey indicates that although in general terms producers appear to be able to rear more pigs without incurring damage to the tail, when the damage does occur, it is severe. We think there could be a number of reasons why this has happened. First, the recent improvement in the proportion of pigs with no damage could be due to increasing awareness by producers of the risk factors when it comes to tail biting. Animal Health Ireland commenced their Pig Tail inspection programme in 2019, and since then all farms in the country were inspected by a trained vet, most on at least 2 occasions, and provided with a personalised report highlighting some of the specific risk factors present on that farm. The risks associated with thermal comfort, animal health, competition for resources and pen design all decreased between the first and second inspections that were carried out. Reduction in risks that could cause chronic stress are likely to reduce the performance of low level biting.
Nevertheless, the increase in severe lesions, or scarring, indicates that a relatively higher proportion of pigs were more than likely exposed to tail biting ‘outbreaks’, which are difficult to control and involve severe tissue damage. It is quite likely that the impact of the Covid-19 pandemic could have contributed to this, as pigs backed up on farms due to slaughterhouse staffing issues, and high stocking densities are one of the most significant risk factors for outbreaks.
There is however, currently significant variation across farms when it comes to level and severity of tail damage. In the most recent survey, the proportion of pigs with perfect tails varied from 12.9% to 79.1%. Likewise, the proportion of pigs with severe tail damage ranged from 0% to 24%. This indicates that some producers are able to highly successfully manage their pigs to minimise biting; the two farms that had no pigs with severe lesions, also had the highest proportion of pigs with no damage at all on their tails. This suggests that at least when it comes to pigs with docked tails, there are solutions that are feasible in typical Irish pig production systems when it comes to minimising the performance of tail biting.
How does this impact you?
In an era of ever-increasing cost and price volatility and tightening profit margins, it is worth reviewing the scale of the economic losses incurred because of tail biting. Carcasses with severe tail lesions are on-average 12kg lighter than unaffected carcasses; even carcasses with mild to moderate tail lesion scores are 1 – 3.6kg lighter than unaffected carcasses. In the slaughterhouse based work carried out in 2014, losses associated with entire and partial condemnations, trimming of the carcass and lower sale weight associated with lesions caused by tail biting on-farm contributed to a 43% erosion of the profit margin per pig.
More recently, we used the Teagasc Pig Production Model to determine the on-farm economic implications of severe tail lesions. We established that farms with over 0.86% of pigs affected with severe tail lesions in the finisher stage incur significantly higher financial losses compared to farms with £ 0.86% pigs affected with severe tail lesions. This was due to a 4.8% decrease in ADG in farms with the higher proportion of bitten tails, translating into 7 days more to reach the target slaughter weight. This resulted in 3.6% more weaner and 1.4% more finisher feed per year, increasing feed costs by 1.5% overall. To put this into perspective, 12 out of the 22 farms in our most recent survey had more than 0.86% of pigs with these severe lesions, and so likely experienced up to a 15% reduction in mean annual profit compared with farms that had a level of tail biting below the threshold of 0.86%.
Interestingly, recent work in collaboration with researchers from Chile revealed that carcasses from pigs affected by tail lesions have a lower muscle pH than carcasses with no other health/welfare problems. The stress associated with being tail bitten could explain this finding. Finnish researchers report that tail-bitten pigs are more prone to stress just before slaughter, reflected in higher blood lactate concentration at slaughter in tail bitten pigs, and ultimately associated with lower initial muscle pH value.
What next?
Tail biting is multifactorial which makes it unpredictable and difficult to control. The only way to manage it is to identify the risk factors on your farm. As the main risk factor – the pigs tail – is not present, the next most important risk factors will always be associated with management and housing practices. Although they vary from farm to farm, it is generally accepted that they are associated with anything that causes increased stress in the pig pen. We recently commenced a study trialling a detailed risk assessment protocol, that we hope will help producers to identify the main risks present on their farm. Farm visits have started, but we are looking for more volunteers, so please get in contact with Roberta D’Alessio if you would like to take part. In tandem, we are also inspecting the condition of pig’s ears on each farm that we visit, as we aim to also elucidate the factors that influence development of ear necrosis. In the next newsletter, we will provide an overview of the main risk factors for tail biting, and what to do in the case of an outbreak.